1. Field of the Invention
The present invention relates to a sputtering apparatus, a method for forming a coating film by sputtering, and a decorated product, and in particular, to a sputtering apparatus capable of advantageously forming a coating film made of a metallic film on a surface of a substrate by sputtering, an advantageous method for forming such a coating film, and a decorated product in which such a coating film is formed on the substrate.
2. Description of the Related Art
Conventionally, decorated products each provided with decoration that provides a metallic surface in appearance by forming a metallic coating film on a substrate comprised of a resin molded article or the like have been broadly used, for example, as skin materials or parts of various products and items such as automobile interior parts, furniture, building materials, home electric appliances, and mobile electronic apparatuses, as alternatives to real metal products.
Such a decorated product is generally produced by forming a coating film or an ink layer comprised of metallic paint or a metallic ink on a coating surface (for example, design surface) of the substrate on which a coating film is to be formed by coating, printing or the like, or produced by plating the coating surface. However, a decorated product having a metallic coating film or a metallic ink layer formed on its coating surface contains a resin material in the coating film or the ink layer. Therefore, it is inevitable that such a decorated product is inferior in brightness compared to real metal. Furthermore, in a decorated product having a plating film formed on a coating surface of a substrate, the plating film is formed to have a relatively large film thickness ranging from several tens micrometers to several hundreds micrometers. Therefore, in such a plated product, a corner part or an edge has a rounded shape, and hence a sharply angular shape of a corner part or an edge of a metallic product is not obtained in the plated product. Therefore, it was difficult to sufficiently obtain a metallic surface that provides a real metallic surface satisfactorily by any of decorated products having a metallic coating film, metallic ink layer, plating film or the like on a coating surface of a substrate.
Under such a circumstance, a technique of obtaining a decorated product by forming a coating film made of a metallic film by sputtering on a coating surface of a substrate is proposed (for example, see JP-A-2004-174921). In this technique, a sputtering apparatus having a vacuum chamber is used. Inside the vacuum chamber, a substrate and a sputtering target made of a film deposition material are disposed so as to be opposed to each other with a predetermined distance therebetween. In such a condition, high energy particles such as ions of inert gas are brought into collision with the sputtering target to allow sputtering particles such as atoms and ions constituting the sputtering target are emitted or discharged (flied out) from the sputtering target. Then, by adhering and deposing the sputtering particles on the coating surface of the substrate, a coating film of a metallic film of the same material as that of the sputtering target is formed, and thus the decorated product is obtained.
In the decorated product obtained by such a technique using sputtering, a coating film made of a metallic film is formed on the substrate to have a sufficiently smaller film thickness compared to the case where the coating film is formed by a plating film. Therefore, a corner part or an edge of the substrate has a sharply angular shape like a corner part or an edge of metallic product, and hence metallic surface is expressed more real compared to the decorated products formed with a metallic coating film, a metallic ink layer, a plating film and the like on the substrate.
By the way, in many products having metallic decoration obtained in various techniques as described above, it is often desired that thickness of the coating film formed on the coating surface of the substrate gradually increases or gradually decreases, for example, from the side of a predetermined one end to the side of the other end opposite to the one end in the width direction, for example, in order to improve the appearance by gradation effect, or to obtain metallic shine with varied intensity.
For example, of interior parts of automobile in decorated products used for parts that transmit various illumination light in a vehicle interior, it is sometimes advantageous that the coating film is formed on the coating surface to have such a film thickness that gradually increases or gradually decrease from a predetermined one end side to the other end side, in order to impressively produce light and dark of transmitted beam by gradation effect realized by the difference in film thickness of the coating film. Furthermore, in a decorated product that constitutes a part of an instrument panel of automobile, when the region around the front glass which receives direct sunlight has strong metallic shine, there is a fear that safety is impaired because the light reflected by the region around the front glass hinders the vision of the driver. For this reason, it is desired that film thickness of the coating film formed in such a part of the coating surface situated near the front glass is made small, while film thickness of the coating film formed in the remaining part of the coating surface is made large so that sufficient metallic shine is obtained.
However, it was very difficult to obtain such a decorated product in which thickness of the coating film formed on the coating surface of the substrate gradually increases or decreases from a predetermined one end side to the other end side by a technique using sputtering which is capable of expressing metallic surface more real. This is because in a conventional sputtering apparatus, it was very difficult to control the amount of sputtering particles emitted from the sputtering target and deposited on the coating surface of the substrate, for individual regions in the coating surface.
According to a coating technique or a printing technique, a coating film having gradually increasing or gradually decreasing thickness may be formed on the coating surface of the substrate relatively easily. However, in a decorated product obtained in this manner, a quality essential for a metallically decorated product is not sufficiently ensured because the corner part and the edge have poor sharpness as described above.